Prematurity is the single largest contributor to neonatal mortality (Van den Berg and Oeshsli: Prematurity. In: Bracken, M B (Ed): Perinatal Epidemiology. Oxford Univ Press, London, 1984, p. 69). It has been reported that the premature rupture of the fetal membranes (PROM) is associated with one third of all preterm deliveries and is the third leading cause of perinatal death (Gibbs et al., 1982, Obstet Gynecol 60: 671-79). Microbial invasion of the amniotic cavity followed by intra uterine inflammation has been documented as the major factor associated with the outcome of preterm labor (Gomez et al., 1995, Clin Perinatal 22: 281-342) and is associated with greater than half of the incidences of preterm labor and premature rupture of the fetal membrane. The main morbidities associated with preterm labor include fetal or infant death, respiratory distress, severe intraventricular hemorrhage, necrotizing enterocolitis, and sepsis.
The immune response to microbial invasion of the amniotic cavity is characterized by the infiltration of polymorphonuclear leukocytes (PMNs) into the placental membranes. Acute inflammation of the amniochorion as determined by the presence of PMNs in the fetal membranes (histologic chorioamnionitis) is considered to be a marker of intraamniotic infection. Clinically silent histologic chorioamnionitis is seen in up to 80% of the cases of preterm labor unresponsive to tocolysis, many of which may present no other evidence of disease (Pankuch et al., 1984, Obstet Gynecol 64: 802-806; Cherouny et al., 1993, Am J Obstet Gynecol 253: 9-14).
It is widely accepted that the biomolecular events and pathophysiologic derangements associated with infections are mediated by endogenous products of the host immune response, such as interleukin-1 (IL-1), interleukin-6 (IL-6), interleukin-8 (IL-8) and tumor ecrosis factor-alpha (TNF-xcex1) (Gomez et al, 1995, supra). Maternal tissues (decidua and residual macrophages) and fetal tissues (amniochorion) are rich sources of these proinflammatory cytokines. IL-1, IL-6, and TNF-xcex1 are all capable of activating pathways which lead to increased production of uterotonins such as prostaglandins, endothelins, PAF, etc. IL-8 can attract and activate polymorphonuclear leukocytes leading to an increase in the overall process of inflammation in uterine tissues (Gomez et al., 1995, Clin Perinatol 22: 281-342). TNF-xcex1 can induce prostaglandin production from placental tissue and can induce preterm labor in animals (Casey et al., 1989, J Clin Invest 83: 430-436; Romero et al., 1992, Am J Obstet Gynecol 166: 1576-87). The levels of these proinflammatory cytokines released from human fetal membranes in response to bacterial lipopolysaccharide mimics the levels of these molecules in the amniotic fluid during MIAC (Fortunato et al., 1996, Am J Obstet Gynecol 174: 1855-62).
Although the role of inflammatory cytokines and their possible role in MIAC has been studied extensively, the potential role of the immunomodulatory cytokines in this process has not been established. IL-10 is an immunoinhibitory cytokine produced by T lymphocytes, monocytes and macrophages. Along with proinflammatory cytokines, IL-10 levels have been shown to be increased in the amniotic fluid of women with infection associated preterm labor (Grieg et al., 1995, Am J Obstet Gynecol 173: 1223-27).
There is currently no effective means of reliably preventing preterm labor associated with intraamniotic infection as well as preterm labors associated with unknown etiologies. Antibiotic therapy has been shown to prolong the pregnancies in PROM but not in preterm labor, however, the effect on infant morbidity has been inconsistent and the use antibiotics have achieved only modest success as a treatment modality (see, for example, Mercer et al., 1997, J Am Med Assoc 278: 989-995). In addition, calcium channel blockers, steroids, prostaglandin inhibitors, and xcex2-sympathomimetic drugs are also commonly used to treat patients with infection, preterm labor and premature rupture of the membranes. Although these treatments are capable of inhibiting myometrial contractility, they have proven less than desirable for effectively treating clinical preterm labor and produce toxic side-effects which limit their utility. Accordingly, there is a great need for improved treatment modalities capable of preventing premature rupture of the membranes and preterm labor associated with intraamniotic infection in order to reduce the unacceptably high level of mortality, morbidity and cost resulting from these conditions.
The present invention provides methods and compositions for the prevention and treatment of preterm labor and premature rupture of fetal membranes. In one aspect, the method of the invention comprises inhibiting the upregulated production of certain pro-inflammatory cytokines in amniochorionic membranes, including IL-6, IL-8 and TNF-xcex1, molecules which applicants regards as key proinflammatory cytokines involved in a cascade of cytokine-influenced and cytokine-promoted inflammation and matrix degeneration that ultimately leads to premature rupture of the membranes and preterm labor. In a particular embodiment described herein, IL-10 is used to achieve the inhibition of cytokine production. In a related embodiment, the method of the invention comprises Linhibiting uterine contractility and preterm labor by contacting the amniochorionic membrane with IL-10. The methods of the invention may be particularly useful in preventing infectioniduced preterm labor and premature rupture of fetal membranes as well as preterm labors with a non-infectious etiology.
The invention is based, in part, on discovering that the cytokine interleukin-10 (IL-10) is capable of transcriptionally inhibiting bacterial lipopolysaccharide-induced upregulated expression of IL-6, IL-8 and TNF-xcex1 in amniochorionic membranes in a dose-dependent manner and that this effect is complete at threshold concentrations. In addition, as described in the Examples which follow, IL-10 treatment of pregnant rhesus macaques experimentally induced to enter preterm labor with IL-xcex2 results in an almost complete inhibition of uterine contractility and preterm labor. Treatment with IL-10 in vivo demonstrates safety, efficacy and long half-life. Preferred embodiments of the invention utilize IL-10 or IL-10 activating substances capable of inhibiting infection-induced uterine contractility and preterm labor.